Mareet is actually a giant in the tale of Ramayana (Ramakien). He's the son of Khaknasoon (also a giant) and a relative to Tossakan, the main villain in the story. Tossakan wanted to capture Lady Sita (Sida) so he commanded Mareet to transform himself into bait (as a golden deer). That's why Mareetís depiction is a half giant-half deer creature.